Patients with advanced stage, N-myc amplified neuroblastoma have only a 2-30 percent 3-year progression-free survival. Therapy with surgery, chemotherapy, and purged autologous transplant is often not curative since tumor frequently recurs at the original site of disease or as a consequence of an incompletely purged bone marrow. This proposal describes an approach designed to produce tumor cell-specific cytotoxicity of neuroblastomas overexpressing N-MYC, based on exploiting the function of N-MYC as a transcription factor. The hypothesis to be tested is that the selective induction of transcription by N-MYC of a carboxylesterase gene will produce selective cytotoxicity when tumor cells are exposed to the topoisomerase I inhibitor CPT-11. The rationale for this hypothesis is based upon the observation that carboxylesterases convert the prodrug CPT-11 to its active metabolite SN-38. Specifically, we propose to test whether endogenous overexpression of N-MYC in tumor cells can selectively transactivate the N-MYC-responsive ornithine decarboxylase promoter allowing transcription of a carboxylesterase. When tumor cells overexpressing N-MYC, and therefore the carboxylesterase, are exposed to CPT-11, the drug will be converted to SN-38 and produce tumor-selective cell kill. We will examine the feasibility of this approach as a potential treatment for minimum residual disease and in the purging of marrow for autologous transplant. The goals of this proposal are to determine: 1) the most appropriate form of rabbit liver carboxylesterase for CPT-11 activation; 2) A) that specific expression of carboxylesterase can be achieved in neuroblastoma cells overexpressing N-MYC from N-MYC responsive promoters, and B) that selective expression of carboxylesterase by tumor cells overexpressing N-MYC can convert CPT-11 to SN-38 and produce tumor cell-specific cytotoxicity; 3) whether this approach eradicates residual disease in a xenograft model; 4) A) whether the proposed approach can be used to purge neuroblastoma cells from marrow using a mouse xenograft model, and B) to purge primary neuroblastoma cells from human peripheral stem (CD34+) cells, with minimal toxicity to hematopoietic cells.